When switching between two speed stages of a vehicular automatic transmission is carried out, there must frequently be carried out simultaneously engagement and release of two frictional engaging elements, including a so-called speak clutch for connecting and disconnecting two rotating members and a so-called speak brake for connecting and disconnecting a rotating member and a fixed member. Such a speed shift is referred to as clutch to clutch speed shift.
By way of example, in the vehicular automatic transmission shown in FIG. 1, the speed shift constitutes clutch to clutch speed shift between a forward first speed stage and a forward second speed stage. The vehicular automatic transmission is provided with a torque converter 10, a transmission gear unit 20, a hydraulic control apparatus 30, an electric control apparatus 40 and various sensor groups 50.
The torque converter 10 is provided with a front cover 101 connected to integrally rotate with an engine output shaft, a pump impeller 102 integrally connected to the front cover 101, a turbine runner 103 rotatably arranged relative to the front cover 101 and the pump impeller 102 in a chamber surrounded by the front cover 101 and the pump impeller 102, and a stator 104.
The transmission gear unit 20 is provided with an input shaft 101 connected to integrally rotate with the turbine runner 103 of the torque converter 10, an output shaft 202 rotatably connected to the wheels, a first planetary gear mechanism 203, a second planetary gear mechanism 204 a carrier of which is connected to integrally rotate with a ring gear of the first planetary gear mechanism 203 and a ring gear of which is connected to integrally rotate with a carrier of the first planetary gear mechanism 203, and a gear mechanism 205 rotatably connected with the carrier of the first planetary gear mechanism 203, the ring gear of the second planetary gear mechanism 204 and the output shaft 202. In addition, a first clutch C1 which is a hydraulically-operated frictional engaging element rotatably and selectively connects and disconnects a sun gear of the second planetary gear mechanism 204 and the input shaft 201, a second clutch C2 which is a hydraulically-operated frictional engaging element selectively connects and disconnects the ring gear of the first planetary gear mechanism 203 as well as the carrier of the second planetary gear mechanism 204 and the input shaft 201, a first brake B0 which is a hydraulically-operated frictional engaging element selectively connects and disconnects the sun gear of the second planetary gear mechanism 204 and a fixed member, a second brake B1 which is a hydraulically-operated frictional engaging element selectively connects and disconnects a sun gear of the first planetary gear mechanism 203 and a fixed member, and a third brake B2 which is a hydraulically-operated frictional engaging element selectively connects and disconnects the ring gear of the first planetary gear mechanism 203 as well as the carrier of the second planetary gear mechanism 204 and a fixed member. Both of the clutches C1, C2 and the brakes B0, B1, B2 are of a well-known multiple disk type.
The above-described speed shift unit 20 can carry out speed shift among one rearward speed stage and four forward speed stages. FIG. 2 shows an engaging operation table of the respective clutches and the respective brakes for setting these speed stages. In FIG. 2, notation P designates parking, notation R designates rearward speed stage, notation N designates neutral, notation 1st designates forward first speed stage, notation 2nd designates forward second speed stage, notation 3rd designates forward third speed stage and notation 4th designates forward fourth speed stage, respectively. Further, marked areas designate engaged states and blank areas designate released states.
As is apparent from FIG. 2, speed shift between the forward first speed stage and the forward second speed stage constitutes clutch to clutch speed shift of the first clutch C1 and the second clutch C2. In up shift from the forward first speed stage to the forward second speed stage, the second clutch C2 is switched from release to engagement and at the same time, the first clutch C1 is switched from engagement to release.
Engagement and release of the respective clutches and the respective brakes are executed by controlling four electromagnetic valves provided to the hydraulic control apparatus 30 (SOL1 and SOL2 which are normally-opened valves and SOL3 and SOL4 which are normally-closed valves shown in FIG. 2) in duty control by the electric control apparatus 40. As is well known, the electric control apparatus 40 is constituted by a microcomputer, ROM, RAM, timers, an input interface, an output interface and an electromagnetic valve drive circuit and the electric control apparatus 40 is inputted with signals from the various sensor groups so, for example, an engine rotational speed signal from an engine rotational speed sensor (Ne sensor), a turbine rotational speed signal from a rotational speed sensor (Ni sensor) of the input shaft 201, an output shaft rotational speed signal from a rotational speed sensor (No sensor) of the output shaft 202 and a throttle opening degree signal from a throttle opening degree sensor (.theta. sensor). Further, in FIG. 2, the O marks related to operational states of the electromagnetic valves indicate a duty ratio of 1.0 and the X marks indicate the duty ratio of 0.0.
FIG. 3 shows a behavior when power on up shift (up shift in the midst of driving a vehicle by engine output) from the forward first speed stage to the forward second speed stage in the vehicular automatic transmission of FIG. 1 is carried out properly.
In FIG. 3, in the forward first speed stage at and before a point in time of issuing the speed shift start instruction (time point t1 of FIG. 3), the released side instruction value (duty ratio provided to electromagnetic valve SOL1) is 0.0, the hydraulic pressure of the first clutch C1 which is the clutch on the released side is at a predetermined maximum value and the first clutch C1 stays in the engaged state. On the other hand, the engaged side instruction value (duty ratio provided to the electromagnetic valve SOL2) is 1.0, the hydraulic pressure of the second clutch which is the clutch on the engaged side is at a minimum value and the clutch C2 stays in the released state.
When the speed shift start instruction is issued, the engaged side instruction value is changed temporarily to 0.0 to increase the engaged side hydraulic pressure (hydraulic pressure provided to the engaged side clutch C2) as swift as possible and after a predetermined constant period has elapsed (time point A in FIG. 3), the engaged side instruction value is changed to an initial value Ci which is set to be able to shift the speed smoothly. On the other hand, the released side instruction value is maintained at 0.0 during a time period in which a release awaiting time period of tr has elapsed from issuance of the speed shift start instruction and when the release awaiting time period tr has elapsed (time point t2 in FIG. 3), the released side instruction value is changed to 1.0 to reduce the released side hydraulic pressure (hydraulic pressure provided to the released side clutch C1) as swift as possible.
Further, when idle run of the piston of the engaged side clutch C2 has been finished and the engaged side hydraulic pressure starts increasing (time point B of FIG. 3), transmission torque is generated at the engaged side clutch C2. Thereafter, the transmission torque of the engaged side clutch C2 is increased in proportion to an increase in the engaged side hydraulic pressure as shown by D of FIG. 3. The rotational speed of the engaged side clutch C2 becomes lower than the rotational speed of the released side clutch C1 by a difference in gear ratios and accordingly, the transmission torque of the engaged side clutch C2 is operated on the reduced speed side, the output shaft torque To of the transmission gear unit is reduced as shown by E in FIG. 3, and a change rate of input shaft rotational speed Ni is reduced as shown by F in FIG. 3. A change rate of the output shaft torque To and a change rate of the input shaft rotational speed Ni are in a proportional relationship. On the other hand, although the released side hydraulic pressure is reduced, the released side clutch C1 is still in the engaged state and no slip is caused. Transmission torque of the released side clutch C1 is reduced by an increase in the transmission torque of the engaged side clutch C2 in accordance with the increase in the transmission torque of the engaged side clutch C2 as shown by G in FIG. 3.
When the transmission torque of the released side clutch C1 becomes null and the released side clutch C1 starts slipping (time point t4 of FIG. 3), the input shaft rotational speed Ni becomes lower than the rotational speed determined by the output shaft rotational speed No and a gear ratio of the forward first speed stage. From when the input shaft rotational speed Ni is detected to be lower than the rotational speed determined by the output shaft rotational speed No and the gear ratio of the forward first speed stage to when the input shaft rotational speed Ni coincides with the rotational speed determined by the output shaft rotational speed No and a gear ratio of the forward second speed stage (time point t5 of FIG. 3), the engaged side instruction value is feed back controlled such that the input shaft rotational speed Ni is reduced while maintaining the change rate of the input shaft rotational speed Ni at a predetermined change rate.
A pattern control is carried out from the time point t1 to the time point t4 of FIG. 3. When the input shaft rotational speed Ni is detected to coincide with the rotational speed determined by the output shaft rotational speed No and the gear ratio of the forward second speed stage, the engaged side instruction value is changed to 0.0, the engaged side hydraulic pressure is increased to a predetermined maximum value and the speed shift is finished.
In FIG. 3, a time period from the point where the transmission torque of the engaged side clutch C2 is generated to the time point where the input shaft rotational speed Ni becomes lower than the output shaft rotational speed No and the gear ratio of the forward first speed stage, is referred to as a torque phase. A time period from the point where the input shaft rotational speed Ni becomes lower than the rotational speed determined by the output shaft rotational speed No and the gear ratio of the forward first speed stage to the point where the input shaft rotational speed Ni coincides with the rotational speed determined by the output shaft rotational speed No and the gear ratio of the forward second speed stage, is referred to as an inertia phase.
In the mass production of constituent elements of the vehicular automatic transmission, a dispersion in a piston idle running distance and a dispersion in properties (correlation between instructed values and hydraulic pressure) of electromagnetic valves provided with control instruction values, are inevitable.
In the case in which the piston idle running distance of the engaged side clutch is shorter than a reference value, when clutch to clutch speed shift is executed at respective reference values of the release awaiting time period tr and the initial value Ci (the reference value of the release awaiting time period tr is adaptable when the piston idle running distance is at its reference value and the reference value of the initial value Ci is adaptable when the property of the electromagnetic valve SOL1 is at its reference property), considerable speed shock is caused. A behavior of speed shift in this case is shown by FIG. 4. In FIG. 4, the bold line indicates a proper case and a dotted line indicates a case in which the speed shift shock is caused. As shown in FIG. 4, at the time point where the piston idle running of the engaged side clutch C2 has been finished, the engaged side hydraulic pressure starts increasing and the transmission torque of the engaged side clutch C2 is generated, thus causing a shift in the hydraulic pressure from point a to point a'. At the time point a', the released side hydraulic pressure does not start reducing and accordingly, the amount of overlapping of the transmission torque of the released side clutch C1 and the transmission torque of the engaged side clutch C2 becomes excessively large and the amount of reduction of the output shaft torque To becomes large as shown by b and considerable speed shift shock is caused.
Further, also in the case in which the property of the electromagnetic valve SOL1 provided with the engaged side instruction value is a property deviated to a side in which the hydraulic pressure relative to the instruction value is increased in view of the reference property, when clutch to clutch speed shift is executed at respective reference values of the release awaiting time period tr and the initial value Ci, considerable speed shift shock is caused. A behavior of the speed shift in this case is shown by FIG. 5. In FIG. 5, the bold line indicates a proper case and the dotted line indicates the case in which the speed shift shock is caused. As shown by FIG. 5, an increase in the engaged side hydraulic pressure after finishing the piston idle running of the engaged side clutch C2 is fast as shown by C and accordingly, the speed of reducing the output shaft torque To becomes fast as shown by d compared with that in the proper case. Further, a reduction in the released side hydraulic pressure cannot follow the increase in the engaged side hydraulic pressure and so the amount of reduction of the output shaft torque To becomes as large as e compared with that in the proper case. Further, even when the operation shifts to the inertia phase, the engaged side hydraulic pressure becomes as high as f compared with that in the proper case and accordingly, a change in the input shaft rotational speed Ni becomes as fast as g compared with that in the proper case. accordingly, the output shaft torque To is rapidly increased as shown by h. In this way, the considerable speed shift shock is caused by rapidly changing the output shaft torque To from the torque phase to the inertia phase.
A state in which engagement of the engaged side clutch C2 is excessively faster than the release of the released side clutch C1 as shown by the dotted lines of FIG. 4 and FIG. 5, is referred to as torque interference (or possibly also referred to as tie up).
Known technology for restraining the above-described torque interference from occurring is described in Japanese Patent Laid-Open No. 341527/1994. According to this known technology, attention is paid to the fact that a time period of the torque phase when speed shift by which the torque interference is caused is carried out becomes longer than a time period of the torque phase when the speed shift is carried out properly in performing clutch to clutch speed shift, a time period T from start of the torque phase to start of the inertia phase in the speed shift operation is detected. When the time period T is longer than a first predetermined time period and shorter than a second predetermined time period, the torque interference is determined to be caused. In clutch to clutch speed shift at the next time, the instruction values are corrected by predetermined amounts such that overlapping of torques allocated to a frictional engaging element on a released side and a frictional engaging element on an engaged side is released, further, when the time period T is longer than the second predetermined time period, strong torque interference is determined to be caused and the hydraulic instruction values are corrected at once such that an increase in transmission torque of the frictional engaging element on the engaged side is restrained. The timing for starting the torque phase is detected by a slight reduction in a differential value of an output shaft rotational speed in a transmission gear unit. Further, the timing of starting the inertia phase is detected by a change in a turbine rotational speed (input shaft rotational speed).
In FIG. 4, the time period T of the torque phase in carrying out speed shift by which torque interference is caused, becomes longer than a time period t of the torque phase when proper speed shift is carried out. Accordingly, when the torque interference is determined by using the method of determining the torque interference described in the publication and the torque interference is determined, the torque interference can be restrained by correcting the engaged side instruction value to a side where the hydraulic pressure is reduced in clutch to clutch speed shift the next time.
In this case, it is important to precisely detect the timing of starting the torque phase. However, according to the detection method in which the torque phase is determined to start by a slight reduction in the differential value of the output shaft rotational speed (change rate of output shaft rotational speed) as described in the publication, it is difficult to precisely detect the timing of starting the torque phase. That is, a differential value of the rotational speed of an output shaft or a turbine in power on up shift, includes also an acceleration component of a vehicle and it is realistically difficult to detect the slight change accompanied by the start of the torque phase.
Further, in FIG. 5, the time period T of the torque phase when speed shift is carried out such that torque interference is caused, becomes shorter than the time period t of the torque phase when proper speed shift is carried out. Therefore, according to the method of determining the torque interference described in the publication, the occurrence of the torque interference cannot be determined.
Therefore, according to the technology described in the aforementioned publication, speed shift shock caused by torque interference in the clutch to clutch speed shift cannot be relatively precisely restrained.
A need thus exists for a detection method capable of relatively precisely detecting the timing of the start of the torque phase in clutch to clutch speed shift.
A need also exists for a speed shift control apparatus of a vehicular automatic transmission that is capable of relatively precisely restraining speed shift shock caused by torque interference in clutch to clutch speed shift.
It would also be desirable to provide a detection method capable of relatively precisely detecting the torque interference intensity in clutch to clutch speed shift.
Further a need exists for a speed shift control apparatus of a vehicular automatic transmission capable of relatively precisely restraining speed shift shock caused by torque interference in clutch to clutch speed shift.